Scrubber discharge bans would protect oceans

5 laboratory bottles with differently coloured liquid from transparent to brown-black.Click to enlarge
All scrubber discharge samples from the measurement campaign are contaminated with pollutants.
Source: Bundesamt für Seeschifffahrt und Hydrographie (BSH)

The German Environment Agency has commissioned a project to study the effects of discharge water from exhaust gas cleaning systems (scrubbers) of ships on the marine environment. Scrubber discharge contains pollutants such as heavy metals and polycyclic aromatic hydrocarbons, which are classified as extremely hazardous. Discharge bans - at least regional - are recommended.

On behalf of the German Environment Agency (UBA), the Federal Maritime and Hydrographic Agency (BSH) and other partners investigated the pollution load and ecotoxicological effects of discharge samples from four ships in the project "Environmental Impacts of Discharge Water from Exhaust Gas Cleaning Systems on Ships (ImpEx)" in the period from 2020 to 2023.

Both water-soluble and particle-bound pollutants were recorded. In particular, vanadium, nickel, copper, iron and zinc as well as polycyclic aromatic hydrocarbons (PAHs) accumulate in the scrubbers' discharge and can lead to genetic mutations or poisoning in marine organisms.

In laboratory tests, the total toxicity of the discharge was examined on marine luminescent bacteria, algae and copepods. The result showed that, depending on the scrubber system, the wastewater can be rated as "practically non-toxic" to "highly toxic" and "extremely toxic". In addition, specific tests were carried out for mutagenic and dioxin-like effects, which were also detected in many samples.

Discharge bans for scrubber discharge water recommended

The results justify the urgent need for action: As a first measure, the BSH proposes to impose a discharge ban in Particular Sensitive Sea Areas (PSSA) and/or coastal areas. A global ban on discharging scrubber discharge into the marine environment is assessed as a measure that can only be implemented in the long term, as decisions for supraregional marine areas are taken at international level in the International Maritime Organization (IMO). In order to push this process, the study results were submitted to the responsible Marine Environmental Protection Committee (MEPC) of IMO. UBA is advocating for a reduction of scrubber discharge there as well as at regional level (Baltic Marine Environment Protection Commission – HELCOM and Committee for the Protection of the Marine Environment of the North-East Atlantic - ⁠OSPAR⁠) and nationally within the framework of the programme of measures for the North Sea and Baltic Sea for the implementation of the European Marine Strategy Framework Directive (MSFD).

Scrubber technology shifts pollutants from air to water

Scrubbers are exhaust gas cleaning systems (EGCS) approved as an alternative to low sulphur fuel oil for seagoing ships. Seawater is sprayed into the exhaust gas to wash out the sulphur. In addition to the washed-out sulphur, other pollutants such as heavy metals, oil residues and also polycyclic aromatic hydrocarbons (PAHs) get into the wastewater. This water mixture of partly long-lived and carcinogenic pollutants is often discharged into the sea almost unpurified and thus pollutes the marine environment.

Today, about 25 per cent of the world merchant fleet (based on the deadweight tonnage of the ships) use scrubbers. This allows ships to continue to run on low-cost heavy fuel oil. In the "open-loop" scrubber process, seawater is used and discharged directly back into the ocean. In the "closed-loop" system, the water is used several times, partially cleaned and can be stored on board in tanks for a certain period of time. If this discharge water is not disposed of in the harbour, but is discharged outside of prohibited zones, it is feared that hot spots, areas with particularly high pollution levels, will develop there.

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 Ships  EGCS  discharge water  water pollutants  North Sea  Baltic Sea  PAH